Add approved AI-enhanced artwork and staging pipeline

[genixpro]

#218 and #219 are now merged. This PR targets master and contains only the remaining AI/material artwork and pipeline changes; there are no engine/test-code changes in its diff. Pack, source-hash and terrain/water validations pass after retargeting.

Part 3 of the #207 split. Adds the approved AI-derived artwork where usable originals are unavailable, on top of the separate original-artwork PR. The 60 original-source runtime frames are unchanged.

Adds 116 AI-upscaled frames, 273 generated-material terrain/water frames and 38 non-AI resampled masks, plus complete padded atlases. Production inputs stay physically separated by origin; data/highres/v1 is the assembled runtime output. All runtime PNGs match the former combined #207 exactly.

A focused staging-only Real-ESRGAN candidate tool fills invisible RGB, pads inference inputs, restores broad source color, and preserves separate base/team alpha. It never automatically promotes candidates. Normal packaging reproduces approved finals exactly; new model inference does not promise bit-exact historical finishing. Historical trial images, rejected variants, model weights and experiment archives remain excluded.

Validation: full pack dimensions, hashes, all resource atlas levels, 91,136 terrain joins and periodic water checks pass. Candidate preparation passes; external model inference was not rerun for this split. The freshly built rebased engine passes gameplay/editor/replay integration and software checks with the combined pack. Original-frame and connected-terrain inputs are rejected by the candidate tool; paired base/team preparation passes. Final before/after comparisons and in-game screenshots are retained.

Units stay with #201. AI consistency, dense-map performance and broader platform review remain open. This can be reviewed independently of accepting the original-source artwork.

Review stack

1. Add high-resolution rendering support and shared map zoom #218 — engine support and zoom
2. Organize original artwork and ship original-derived HD sprites #219 — original sources and original-derived artwork (base: Add high-resolution rendering support and shared map zoom #218)
3. Add approved AI-enhanced artwork and staging pipeline #220 — AI-enhanced finals and candidate pipeline (base: Organize original artwork and ship original-derived HD sprites #219)

After a parent merges, retarget its child to master. #207 retains the prior discussion and is superseded by this stack.

Scope and build guide.

Final before/after gallery.